The central role of excitatory amino acids as neurotransmitters, neuromodulators and as mediators of neuropathological processes is now widely accepted. Specifically, receptors and ion channels activated by L-glutamate and related endogenous excitatory amino acids may play a role in synaptic plasticity in the hippocampus and integration of both sensory and motor information in the spinal cord; current hypotheses of the pathogenesis of neuronal cell death in stroke, Huntington's disease, Alzheimer's, spinocerebellar degenerations and seizure- related brain damage also rely in part of 'excessive' activation of these same receptors. The broad objective of this project is to explore the cellular and molecular mechanisms by which excitatory amino acids exert their effects with a particular focus on the role of the N-methyl- D-aspartate (NMDA) receptor subtype in synaptic transmission. This unique agonist-gated channel has two features - voltage- dependence and calcium permeability - which make this channel an excellent candidate as a modulator of neuronal excitability. The general strategy will be to explore, using electrophysiological methods, the properties of L-glutamate activated ion channels which are likely to contribute to excitatory synaptic efficacy. In particular the contribution of second messenger activation, desensitization and agonist-gated transmembrane calcium influx on agonist-evoked responses and on single excitatory synapses will be examined. The relevance to synaptic transmission and drug action of three modulatory binding sites (Mg, Zn and glycine) on the NMDA receptor channel will also be examined. These three potent endogenous modulators have the capability to regulate ion flux through NMDA-receptor channels, and underscore the potential for pharmacological action at NMDA receptors. The experimental approach will use voltage and patch clamp methods on primary dissociated neurons in cultures prepared from rodent central nervous system, primarily hippocampus. Significant effort will be directed to preparations allowing study of identified cells types, and microisland cultures to allow study of single excitatory synapses.